The cellular slime mold, Dictyostelium discoideum is an ideal experimental organism for research in developmental biology. The vegetative stage consists of amoeboid cells which subsequently aggregate in response to the chemotactic substance cyclic AMP. The multicellular pseudoplasmodia undergo a series of morphogenetic movements which are accompanied by cell differentiation. These events result in the formation of a fruiting body composed of a slender stalk supporting a mass of spores. Unless aggregation and consequently cell adhesion occurs cell differentiation does not occur. Cell adhesion depends upon major ultrastructural changes in the plasma membranes. These adaptations enable contacts to occur between apposing cells which result in the interactions required to effect differentiation. The major objectives in the research include determining the nature of the ultrastructural and molecular compenents in the plasma membranes which form the basis for adhesiveness. Labeled oligosaccharide sugars will be utilized to determine if the onset of cell adhesion at aggregation is associated with major changes in the glycoprotein content of the plasma membranes. Aggregateless mutants which fail to acquire adhesiveness or differentiate will be used comparatively in appropriate experiments. In addition the specific cytoplasmic events related to cell differentiation which result from the cell-cell contacts will be investigated by the use of labeled sugars. The role of the plasma membranes in cell interactions will be approached by modifying the degree of cell contacts and observating the effect upon cell differentiation. The contacts will be modified by enzymes, specific antibodies, N-acetyl-D-galactosamine or mechanical dispersal into monolayers of contacting or non-contacting cells. The ability of cells to differentiate under these circumstances will be monitered by the use of oligosaccharide sugars such as 3H-L-fucose. This sugar is incorporated specifically into differentiating prespore cells but not into prestalk cells and consequently can be utilized to determine the state of differentiation of a cell by autoradiographic procedures. It is anticipated that these studies will yield information concerning the role of the plasma membranes in cell differentiation.